Display device

ABSTRACT

A display device includes a display substrate including at least one step portion, and a thin film encapsulation layer above the display substrate, the thin film encapsulation layer including a buffer layer configured to reduce a height difference due to the at least one step portion and a barrier layer above the buffer layer, the buffer layer including a plurality of sub-layers and interfaces between the plurality of sub-layers, and the interfaces including a curved surface changing from a concave shape to a convex shape toward a portion overlapping the step portion from an outer portion of the step portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/334,181, filed Oct. 25, 2016, which claims priority to and thebenefit of Korean Patent Application No. 10-2016-0027699, filed on Mar.8, 2016, in the Korean Intellectual Property Office, the disclosure ofall of which is incorporated herein in its entirety by reference.

BACKGROUND 1. Field

Aspects of the present invention relate to a display device.

2. Description of the Related Art

As a display field visually expressing various kinds of electric signalinformation develops rapidly, various flat panel display devices havingexcellent characteristics, such as a slim profile, a light weight, andlow power consumption are introduced, and furthermore, flexible displaydevices are being researched and developed.

A display device having a slim profile and a flexible characteristic mayinclude a thin film encapsulation layer in order to block penetration ofmoisture, oxygen, and/or the like from outside. A general thin filmencapsulation layer has a configuration in which inorganic layers andorganic layers are alternately stacked. However, because the organiclayer and the inorganic layer are manufactured via different processesin different chambers, a process of manufacturing the thin filmencapsulation layer is complicated and impurities may be introduced intothe thin film encapsulation layer during transfer between the chambers,causing the thin film encapsulation layer to become damaged.

SUMMARY

Aspects of some embodiments of the present invention are directed to adisplay device that includes a thin film encapsulation layer havingdesirable (e.g., excellent) characteristics, such as a slim profile, alight weight, and low power consumption, and which is manufactured by asimple process.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more embodiments of the present invention, there isprovided a display device including: a display substrate including atleast one step portion; and a thin film encapsulation layer above thedisplay substrate, the thin film encapsulation layer including a bufferlayer configured to reduce a height difference due to the at least onestep portion and a barrier layer above the buffer layer, the bufferlayer including a plurality of sub-layers and interfaces between theplurality of sub-layers, and the interfaces including a curved surfacechanging from a concave shape to a convex shape toward a portionoverlapping the step portion from an outer portion of the step portion.

In an embodiment, each of the plurality of sub-layers has a thicknessfrom about 300 Å to about 10000 Å.

In an embodiment, an interval between two adjacent interfaces of theinterfaces increases toward the display substrate in the outer portionof the step portion.

In an embodiment, an interval between two adjacent interfaces of theinterfaces reduces toward a portion overlapping the step portion fromthe outer portion of the step portion.

In an embodiment, the buffer layer has a first thickness at a locationspaced from the step portion and has a second thickness at a locationoverlapping the step portion, and wherein the second thickness is about0.5 times or more than and less than about one times the firstthickness.

In an embodiment, the plurality of sub-layers include a silicon oxideincluding carbon and hydrogen, and each of the plurality of sub-layersincludes about 20 to about 50 atomic % of silicon, about 10 to about 40atomic % of oxygen, and about 30 to about 60 atomic % of carbon based ona total number of atoms of the silicon, the oxygen, and the carbon.

In an embodiment, each of the plurality of sub-layers includes a firstregion and a second region above the first region, an upper surface ofthe second region forming an interface of the interfaces, and the secondregion has a silicon content ratio greater than that of the firstregion, and the second region has a carbon content ratio less than thatof the first region.

In an embodiment, each of the plurality of sub-layers includes about 30to about 40 atomic % of the silicon, about 18 to about 28 atomic % ofthe oxygen, and about 40 to about 50 atomic % of the carbon based on atotal number of atoms of the silicon, the oxygen, and the carbon.

In an embodiment, each of the plurality of sub-layers includes about 33to about 36 atomic % of the silicon, about 20 to about 23 atomic % ofthe oxygen, and about 42 to about 45 atomic % of the carbon based on atotal number of atoms of the silicon, the oxygen, and the carbon.

In an embodiment, the display substrate includes a base substrate and adisplay portion above the base substrate, the display portion includes aplurality of display elements and a pixel-defining layer defining alight-emitting region of the plurality of display elements, and the atleast one step portion includes the pixel-defining layer.

In an embodiment, the display device further includes a protective layerabove the display portion, the protective layer including a samematerial as that of the buffer layer.

In an embodiment, each of the plurality of display elements includes afirst electrode, a second electrode, and an intermediate layer betweenthe first and second electrodes, the intermediate layer including anorganic emission layer, and the display substrate further includes acapping layer between the first electrode and the protective layer, thecapping layer having a refractive index greater than that of theprotective layer.

In an embodiment, the protective layer has a refractive index from about1.38 to about 1.5.

In an embodiment, the protective layer further includes silicon carbideto which hydrogen is coupled.

In an embodiment, the thin film encapsulation layer is configured toseal the display portion, the barrier layer includes a first barrierlayer and a second barrier layer overlapping each other with the bufferlayer therebetween, and the first and second barrier layers include aninorganic layer.

In an embodiment, the first and second barrier layers contact each otherat an outer portion of the buffer layer.

According to one or more embodiments of the present invention, there isprovided a method of manufacturing a display device, the methodincluding: forming a display portion above a base substrate; and forminga thin film encapsulation layer sealing the display portion, the formingof the thin film encapsulation layer including: injecting a raw gas anda reaction gas inside a chamber in which the base substrate is located,depositing a precursor layer above the base substrate by utilizingplasma-enhanced chemical vapor deposition, and forming a sub-layer bycuring the precursor layer utilizing plasma; forming a plurality ofsub-layers and forming a buffer layer in which the plurality ofsub-layers are stacked; and forming a barrier layer above the bufferlayer inside the chamber, wherein the plurality of sub-layers include asilicon oxide including carbon and hydrogen, and wherein each of theplurality of sub-layers include about 20 to about 50 atomic % ofsilicon, about 10 to about 40 atomic % of oxygen, and about 30 to about60 atomic % of carbon based on a total number of atoms of the silicon,the oxygen, and the carbon.

In an embodiment, the raw gas includes hexamethyldisiloxane, and thereaction gas includes oxygen, nitrous oxide, and/or hydrogen.

In an embodiment, the buffer layer includes interfaces between theplurality of sub-layers, each of the plurality of sub-layers includes afirst region and a second region above the first region, an uppersurface of the second region forming an interface of the interfaces, thesecond region has a silicon content ratio greater than that of the firstregion, and the second region has a carbon content ratio less than thatof the first region.

In an embodiment, each of the plurality of sub-layers includes about 30to about 40 atomic % of the silicon, about 18 to about 28 atomic % ofthe oxygen, and about 40 to about 50 atomic % of the carbon based on atotal number of atoms of the silicon, the oxygen, and the carbon.

In an embodiment, each of the plurality of sub-layers includes about 33to about 36 atomic % of the silicon, about 20 to about 23 atomic % ofthe oxygen, and about 42 to about 45 atomic % of the carbon based on atotal number of atoms of the silicon, the oxygen, and the carbon.

In an embodiment, the display portion includes at least one step portionabove a surface thereof, and the buffer layer has a first thickness at alocation spaced from the step portion and a second thickness at alocation overlapping the step portion, the second thickness being about0.5 times or more than and less than about one times the firstthickness.

In an embodiment, the interfaces are formed in a curved surface changingfrom a concave shape to a convex shape toward a portion overlapping thestep portion from an outer portion of the step portion.

In an embodiment, an interval between two adjacent interfaces of theinterfaces increases toward the display portion in an outer portion ofthe step portion.

In an embodiment, an interval between two adjacent interfaces of theinterfaces reduces toward a portion overlapping the step portion from anouter portion of the step portion.

In an embodiment, each of the plurality of sub-layers has a thicknessfrom about 300 Å to about 10000 Å.

In an embodiment, the method further includes: before the forming of thethin film encapsulation layer, forming a protective layer above thedisplay portion, wherein the protective layer includes a same materialas that of the sub-layer and being formed by utilizing a same method asthe sub-layer, and wherein flux of oxygen introduced into the chamberwhile the protective layer is formed is greater than that of oxygenintroduced into the chamber while the sub-layer is formed.

In an embodiment, the protective layer further includes silicon carbideto which hydrogen is coupled.

In an embodiment, the protective layer has a refractive index from about1.38 to about 1.5.

In an embodiment, the display portion includes a plurality of displayelements, each including a first electrode, a second electrode, and anintermediate layer between the first and second electrodes, theintermediate layer including an organic emission layer, and wherein thedisplay device includes a capping layer between the second electrode andthe protective layer, the capping layer having a refractive indexgreater than that of the protective layer.

Thus, according to some embodiments of the present invention, a thinfilm encapsulation layer includes a buffer layer, so that a barrierlayer may be prevented or substantially prevented from being damaged bya step difference caused by impurities, and/or the like, and thus acharacteristic of the thin film encapsulation layer may improve. Also,because the buffer layer and the barrier layer are manufactured by thesame process, manufacturing efficiency of a display device may improve(e.g., increase). As understood by a person of ordinary skill in theart, the scope of the inventive concept is not limited by this effect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a plan view illustrating a display device according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating an example of a portion ofthe display device taken along the line I-I′ of FIG. 1;

FIG. 3 is a magnified view illustrating a portion A of the displaydevice of FIG. 2;

FIG. 4 is a graph illustrating composition of a sub-layer versus alocation of the sub-layer of FIG. 3;

FIG. 5 is a flow diagram illustrating a process of manufacturing adisplay device of FIG. 1;

FIG. 6 is a cross-sectional view illustrating another example of theportion of the display device taken along the line I-I′ of FIG. 1;

FIG. 7 is a cross-sectional view illustrating another example of theportion of the display device taken along the line I-I′ of FIG. 1;

FIG. 8 is a cross-sectional view illustrating another example of theportion of the display device taken along the line I-I′ of FIG. 1;

FIG. 9 is a cross-sectional view illustrating another example of theportion of the display device taken along the line I-I′ of FIG. 1; and

FIG. 10 is a cross-sectional view illustrating an example of a portionof the display device taken along the line II-II′ of FIG. 1.

DETAILED DESCRIPTION

As the inventive concept allows for various suitable changes andnumerous embodiments, exemplary embodiments will be illustrated in thedrawings and described in detail in the written description. However,this is not intended to limit the inventive concept to particular modesof practice, and it is to be appreciated that all changes, equivalents,and substitutes that do not depart from the spirit and technical scopeof the inventive concept are encompassed in the inventive concept. Inthe description of the inventive concept, certain detailed explanationsof the related art are omitted when it is deemed that they mayunnecessarily obscure the essence of the inventive concept.

Hereinafter, the inventive concept will be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the inventive concept are shown. When description is made withreference to the drawings, like reference numerals in the drawingsdenote like or corresponding elements, and repeated description thereofmay be omitted.

FIG. 1 is a plan view illustrating a display device 10 according to anembodiment of the present invention; FIG. 2 is a cross-sectional viewillustrating an example of a portion of the display device 10 takenalong the line I-I′ of FIG. 1; FIG. 3 is a magnified view illustrating aportion A of the display device 10 of FIG. 2; and FIG. 4 is a graphillustrating composition of a sub-layer versus a location of thesub-layer of FIG. 3.

Referring to FIGS. 1 to 4, the display device 10 according to anembodiment may include a display substrate 100 and a thin filmencapsulation layer 200 above the display substrate 100. The thin filmencapsulation layer 200 may include a buffer layer 210 and a barrierlayer 220.

The display substrate 100 may produce an image by including a pluralityof display elements. The display substrate 100 may include varioussuitable kinds of display elements, such as an organic light-emittingdiode (OLED), a light-emitting diode (LED), and a liquid crystal display(LCD). Also, the display substrate 100 may include, on one side, a padportion 150 for transferring an electric signal from a power supply or asignal generator to the plurality of display elements.

The display substrate 100 may include at least one step portion S. Thestep portion S may result from the structure of the display substrate100 or may be formed due to a particle, and/or the like on the surfaceof the display substrate 100.

The step portion S induces a height difference in the surface of thedisplay substrate 100, and when external force is applied to the displaysubstrate 100, stress concentrates on the step portion S, so thatdamage, such as cracks, to the thin film encapsulation layer 200, forexample, the barrier layer 220 above the step portion S may occur. Also,where a contact angle between the step portion S and the displaysubstrate 100 is small (e.g., forms an acute angle, such as where thestep portion S has an inversely tapered shape or the step portion S isformed by particles), the thin film encapsulation layer 200 does notcompletely fill a space between the step portion S and the displaysubstrate 100, and thus an air gap, and/or the like may be generatedbetween the display substrate 100 and the thin film encapsulation layer200. To prevent or substantially prevent the formation of the air gap,the thin film encapsulation layer 200 formed above the display substrate100 may include the buffer layer 210.

The buffer layer 210 may prevent or substantially prevent damage of thebarrier layer 220 due to concentration of stress by a step difference,or when external force is applied, by reducing the step difference ofthe step portion S. The buffer layer 210 completely surrounds the stepportion S, thereby preventing or substantially preventing an air gapfrom being generated between the display substrate 100 and the thin filmencapsulation layer 200 even where a contact angle between the stepportion

S and the display substrate 100 forms an acute angle. Also, the bufferlayer 210 may reduce the stress formed on the barrier layer 220.

The buffer layer 210 may include a plurality of stacked sub-layers 222.The plurality of sub-layers 222 are layers that may be distinguishedfrom (e.g., discriminated from) each other. Interfaces 226 may bebetween the plurality of sub-layers 222.

The plurality of sub-layers 222 may include a silicon oxide includingcarbon and hydrogen. For example, the plurality of sub-layers 222 mayinclude a material having an empirical formula of SiOxCyHz. In thiscase, when a composition ratio of x increases, the plurality ofsub-layers 222 may have properties close to an inorganic layer. When acomposition ratio of y increases, the plurality of sub-layers 222 mayhave properties close to an organic layer.

If the composition ratio of x is excessively large, because theplurality of sub-layers 222 are formed conformally, a step difference(e.g., a step height) of the step portion S may be difficult to reduce,and where a contact angle between the step portion S and the displaysubstrate 100 is small, an air gap may be generated between the displaysubstrate 100 and the thin film encapsulation layer 200. However, if thecomposition ratio of y is excessively large, because a precursor layerfor forming the sub-layer 222 has high liquidity, it may be difficult toform the sub-layers 222 having a constant thickness above the stepportion S. Additionally, when the thickness of the buffer layer 210 isequal to or less than the thickness of the step portion S, if thecomposition ratio of y is excessively large, the buffer layer 210 maynot sufficiently cover the upper portion of the step portion S, andthus, the barrier layer 220 may be damaged by the step portion S.

Therefore, even where the buffer layer 210 has excellent step coverageand a contact angle between the step portion S and the display substrate100 is small, to prevent or substantially prevent generation of an airgap between the display substrate 100 and the thin film encapsulationlayer 200, each of the plurality of sub-layers 222 may include about 20to about 50 atomic % of silicon, about 10 to about 40 atomic % ofoxygen, and about 30 to about 60 atomic % of carbon based on a totalnumber of atoms of the silicon, the oxygen, and the carbon. In anembodiment, each of the plurality of sub-layers 222 may include about 30to about 40 atomic % of silicon, about 18 to about 28 atomic % ofoxygen, and about 40 to about 50 atomic % of carbon. In anotherembodiment, each of the plurality of sub-layers 222 may include about 33to about 36 atomic % of silicon, about 20 to about 23 atomic % ofoxygen, and about 42 to about 45 atomic % of carbon. In this case, aratio of oxygen to silicon (O/Si) may be about 0.4 or more and about 1or less.

Each of the plurality of sub-layers 222 may have a thickness rangingfrom about 300 Å to about 10000 Å. When the thickness of each of theplurality of sub-layers 222 is less than 300 Å, the plurality ofsub-layers 222 cured by plasma have properties close to an inorganiclayer as a whole, and the hardness of the plurality of sub-layers 222increases, thus it may be difficult to distribute stress generated tothe barrier layer 220. However, when the thickness of each of theplurality of sub-layers 222 is greater than 10000 Å, the sub-layers 222may have an uncured portion therein and have an excessively softcharacteristic, so that wrinkles may occur in the plurality ofsub-layers 222 and thus the thin film encapsulation layer 200 has a hazecharacteristic, which may affect the display quality of the displaydevice 10.

The plurality of sub-layers 222 completely surround the step portion S.In this case, the interfaces 226 may include a curved surface changingfrom a concave shape to a convex shape toward a location overlapping thestep portion S from the outer portion of the step portion S. Here, theconcave shape denotes a shape bending toward the display substrate 100,and the convex shape denotes a shape bending away from (e.g., toward theopposite side of) the display substrate 100. Curvature radii having theconcave shape and the convex shape of the interfaces 226 may graduallyincrease the further away they are from the display substrate 100.

For example, in the outer portion of the step portion S, intervals(e.g., gaps or distances) g1 and g21 between two adjacent interfaces 226from among the interfaces 226 may increase (g21>g1) toward the displaysubstrate 100. Intervals g21 and g22 between two adjacent interfaces 226from among the interfaces 226 may reduce (g21>g22) toward a locationoverlapping the step portion S from the outer portion of the stepportion S. Here, the intervals g1 and g21 between the interfaces 226 atthe outer portion of the step portion S may denote a maximum intervalbetween concave shapes of the interfaces 226.

That is, a difference between the thickness g21 at the outer portion ofthe step portion S and the thickness g22 at a location overlapping thestep portion S in one sub-layer 222 increases toward the displaysubstrate 100 and as the height of the step portion S increases. Thedifference may gradually reduce as the sub-layers 222 are stacked.Therefore, initially stacked sub-layers 222 may completely cover thesurface of the step portion S, and fill a gap between the step portion Sand the display substrate 100. As the sub-layers 222 are stacked, a stepdifference (e.g., a step height) of the step portion S reduces and theupper surface of the buffer layer 210 may be planarized or substantiallyplanarized. Also, the buffer layer 210 has a first thickness T1 at alocation spaced apart from the step portion S and a second thickness T2at a location overlapping the step portion S. In this case, the secondthickness T2 may be about 0.5 times or more than, and less than onetimes, the thickness T1.

Each of the plurality of sub-layers 222 may include a first region 223and a second region 224 successively above the first region 223 andincluding an upper surface forming the interface 226. The second region224 is formed while a precursor layer for forming the sub-layer 222 iscured and may have a thickness ranging from about 50 Å to about 1500 Å.

The second region 224 may have a composition different from that of thefirst region 223. FIG. 4 illustrates results obtained by measuring thecontent of carbon 1, oxygen 2, and silicon 3 included in the sub-layer222 at a first location P1, a second location P2, and a third locationP3 of FIG. 3 by using x-ray photoelectron spectroscopy (XPS). Referringto FIG. 4, it is shown that the content of the silicon 3 at the firstlocation P1 is greater than the content of the silicon 3 at the secondand third locations P2 and P3, and the content of the carbon 1 at thefirst location P1 is less than the content of the carbon 1 at the secondand third locations P2 and P3. That is, because a content ratio of thesilicon 3 of the second region 224 is greater than a content ratio ofthe silicon 3 of the first region 223 and a content ratio of the carbon1 of the second region 224 is less than a content ratio of the carbon 1of the first region 223, the second region 224 may have properties closeto an inorganic layer compared to the first region 223. Therefore,because the buffer layer 210 has a structure in which the first region223 and the second region 224 having different properties have a smallthickness and are multi-layered, moisture and oxygen-blockingcharacteristics improve and excellent flexibility may be obtained.

The thin film encapsulation layer 200 includes the barrier layer 220above the buffer layer 210. The barrier layer 220 blocks penetration ofexternal moisture and oxygen, may be larger than the buffer layer 210,may cover the upper surface and the lateral surfaces of the buffer layer210, and contact the display substrate 100 at the outer portion of thebuffer layer 210.

The barrier layer 220 may include silicon nitride, aluminum nitride,zirconium nitride, titanium nitride, hafnium nitride, tantalum nitride,silicon oxide, aluminum oxide, titanium oxide, tin oxide, cesium oxide,silicon oxynitride (SiON), and/or the like.

FIG. 5 is a flow diagram illustrating a method of manufacturing thedisplay device 10 of FIG. 1; and FIG. 6 is a cross-sectional viewillustrating another example of the portion of the display device 10taken along the line I-I′ of FIG. 1.

Referring to FIGS. 1 to 3 and 5, the method of manufacturing the displaydevice 10 may include forming the display substrate 100 (S10) andforming the thin film encapsulation layer 200 above the displaysubstrate 100 (S20 to S40).

As described below with reference to FIG. 7, the display substrate 100includes a base substrate 101 (see, e.g., FIG. 7) and a display portion110 (see, e.g., FIG. 7) formed above the base substrate 101. The displaysubstrate 100 is described below with reference to FIG. 7.

The thin film encapsulation layer 200 may be formed by forming thebuffer layer 210 by repeating operations of depositing a precursor layerabove the display substrate 100 (S20) and forming one sub-layer 222 bycuring the deposited precursor layer (S30), and then by forming thebarrier layer 220 above the buffer layer 210 (S40).

The precursor layer may be formed by injecting a raw gas and a reactiongas into a chamber in which the display substrate 100 is located, andperforming plasma-enhanced chemical vapor deposition (PECVD). The rawgas may be hexamethyldisiloxane, and the reaction gas may be oxygen orhydrogen; however, embodiments of the present invention are not limitedthereto. In an embodiment, the raw gas may be hexamethyldisilazane,tetraethoxysilane, tetramethylcyclotetrasiloxane,octamethylcyclotetrasiloxane, tetramethylsilane, tetramethyldisiloxane,and/or the like.

As an example, when hexamethyldisiloxane is used as the raw gas andoxygen is used as the reaction gas, hexamethyldisiloxane is decomposedon a monomer basis and then a precursor layer having composition ofSiOxCyHz may be deposited as described below.

HMDSO((CH₃)₃Si—O—Si(CH₃)₃))→(CH₃)₃Si—O—Si(CH₃)₂+CH₃→SiO_(x)C_(y)H_(z)+CH_(x′)  Chemicalformula 1

HMDSO((CH₃)₃Si—O—Si(CH₃)₃))→(CH₃)₃Si—O—+—Si(CH₃)₃→SiO_(x)C_(y)H_(z)+SiC_(x″)H_(y)  Chemical formula 2

That is, when hexamethyldisiloxane is decomposed, a carbonate group anda methyl group are formed. In this case, as flux of oxygen, which is thereaction gas, increases, an oxidation reaction is dominant and thecontent of carbon inside the deposited precursor layer may reduce. Whenthe content of carbon inside the precursor layer reduces, the formedsub-layer 222 may have properties close to an inorganic layer.Therefore, the properties of the sub-layer 222 may be adjusted byadjusting the flux of oxygen or replacing oxygen with nitrous oxide whendepositing the precursor layer.

For example, to perform deposition to allow the precursor layer to filla gap between the display substrate 100 and the thin film encapsulationlayer 200 and to have adequate (e.g., excellent) step coverage, the fluxof oxygen introduced into the chamber may be about 100 to about 20000sccm; however, embodiments of the present invention are not limitedthereto. The temperature, pressure, and flux of the raw gas and thereaction gas inside the chamber may be adjusted depending on theproperties of the sub-layer 222 when depositing the precursor layer. Forexample, the flux of oxygen may increase as the number of stacks (e.g.,as the number of times of stacking) of the sub-layers 222 increases.Therefore, an initially deposited precursor layer has improved liquidityand thus may effectively fill a gap between the step portion S and thedisplay substrate 100.

After the precursor layer is deposited, the sub-layer 222 is formed bycuring the precursor layer. The curing of the precursor layer may beperformed by using hydrogen plasma, for example. In an embodiment, thecuring of the precursor layer may be performed by using plasma of oxygenor an arbitrary gas.

The sub-layer 222 may have a thickness ranging from about 300 5< toabout 10000 Å. When the sub-layer 222 has a thickness less than about300 Å, because the hardness of the sub-layer 222 increases due to plasmacuring, it may be difficult to distribute stress occurring in thebarrier layer 220. When the sub-layer 222 has a thickness greater thanabout 10000 Å, the sub-layers 222 may have an uncured portion thereinand have an excessively soft characteristic, so that wrinkles may occurin the sub-layer 222. The sub-layer 222 may be repeatedly formed aplurality of numbers of times. The plurality of stacked sub-layers 222may form the buffer layer 210.

A difference between the thickness g21 at the outer portion of the stepportion S and the thickness g22 at a location overlapping the stepportion S in one sub-layer 222 may increase toward the display substrate100, and gradually reduce as the sub-layers 222 are stacked. Therefore,initially stacked sub-layers 222 completely cover the surface of thestep portion S and fill a gap between the step portion S and the displaysubstrate 100. As the plurality of sub-layers 222 are stacked, a stepdifference (e.g., a step height) of the step portion S reduces and thusthe surface of the buffer layer 210 may be planarized or substantiallyplanarized. In this case, the formed buffer layer 210 has a firstthickness T1 at a location spaced apart from the step portion S and asecond thickness T2 at a location overlapping the step portion S. Here,the second thickness T2 may be about 0.5 times or more than and lessthan one times the thickness T1.

To do so, the sub-layer 222 may include about 20 to about 50 atomic % ofsilicon, about 10 to about 40 atomic % of oxygen, and about 30 to about60 atomic % of carbon based on a total number of atoms of the silicon,the oxygen, and the carbon. In an embodiment, the sub-layer 222 mayinclude about 30 to about 40 atomic % of silicon, about 18 to about 28atomic % of oxygen, and about 40 to about 50 atomic % of carbon. In anembodiment, the sub-layer 222 may include about 33 to about 36 atomic %of silicon, about 20 to about 23 atomic % of oxygen, and about 42 toabout 45 atomic % of carbon. The sub-layer 222 having the abovecomposition may have a modulus ranging from about 2 to about 3 GPa.

FIG. 6 illustrates that the buffer layer 210 surrounds a particle Phaving a circular cross-section. When the buffer layer 210 has the abovecomposition, as illustrated in FIG. 6, the buffer layer 210 completelysurrounds the particle P. Therefore, even where a contact angle betweenthe particle P and the display substrate 100 forms an acute angle, anair gap is not generated below the particle P and a step differencecaused by the particle P reduces, so that stress applied to the barrierlayer 220 formed above the buffer layer 210 may reduce.

The plurality of sub-layers 222 may include the first region 223 and thesecond region 224 directly exposed to plasma during a curing process.The second region 224 is a region in which a content ratio of carbon isreduced by the plasma, and may have properties close to an inorganiclayer compared to the first region 223. Therefore, because the bufferlayer 210 has a structure in which the first region 223 and the secondregion 224 having different properties have a small thickness and aremulti-layered, moisture and oxygen-blocking characteristics improve andexcellent flexibility may be maintained.

The barrier layer 220 may be formed by using the same method of formingthe buffer layer 210 inside the chamber. Therefore, when the thin filmencapsulation layer 200 is formed, tact time may reduce.

FIG. 7 is a cross-sectional view illustrating another example of theportion of the display device 10 taken along the line I-I′ of FIG. 1.

Referring to FIG. 7, the display device 10 may include the displaysubstrate 100 and the thin film encapsulation layer 200 above thedisplay substrate 100. The thin film encapsulation layer 200 may includethe buffer layer 210 and the barrier layer 220. The thin filmencapsulation layer 200 may prevent or substantially prevent externaloxygen and moisture from penetrating into the display portion 110 bysealing the display portion 110. Because the buffer layer 210 and thebarrier layer 220 are the same or substantially the same as thosedescribed with reference to FIGS. 1 to 6, descriptions thereof may notbe repeated.

The display substrate 100 may include the base substrate 101 and thedisplay portion 110 above the base substrate 101. The display portion110 may include a display element 110 b and a thin film transistor (TFT)110 a electrically connected to the display element 110 b. Though anexample in which the display element 110 b includes an organic emissionlayer is described below, embodiments of the present invention are notlimited thereto, and the display element 110 b may include varioussuitable kinds of display elements such as a light-emitting diode (LED),an liquid crystal, and/or the like.

The base substrate 101 may include various suitable materials. Forexample, the base substrate 101 may include a transparent glass materialincluding SiO₂ as a main component. However, the base substrate 101 isnot limited thereto and may include a transparent plastic material. Theplastic material may include an organic material includingpolyethersulfone (PES), polyarylate (PAR), polyetherimide (PEI),polyethylen naphthalate (PEN), polyethyleneterepthalate (PET),polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate(PC), cellulose triacetate (TAC), cellulose acetate propionate (CAP),and/or the like.

A buffer layer 102 may be formed above the base substrate 101. Forexample, the buffer layer 102 may include an inorganic material, such assilicon oxide, silicon nitride, silicon oxynitride, aluminum oxide,aluminum nitride, titanium oxide, titanium nitride and/or the like,and/or an organic material, such as polyimide, polyester, and acryl,and/or the like, and may include a plurality of stacked materials fromamong the above materials.

The TFT 110 a may include an active layer 103, a gate electrode 105, asource electrode 107, and a drain electrode 108. A case where the TFT110 a is a top gate-type TFT in which the active layer 103, the gateelectrode 105, the source electrode 107, and the drain electrode 108 aresequentially formed in this stated order is described below. However,embodiments of the present invention are not limited thereto, andvarious suitable types of TFTs 110 a, such as a bottom type TFT, may beemployed.

The active layer 103 includes a semiconductor material and may include,for example, amorphous silicon, poly crystalline silicon, and/or thelike. However, embodiments of the present invention are not limitedthereto, and the active layer 103 may include various suitablematerials. In an embodiment, the active layer 103 may include an organicsemiconductor material. In another embodiment, the active layer 103 mayinclude an oxide semiconductor material. For example, the active layer103 may include Groups 12, 13, 14 metallic elements, such as Zn, In, Ga,Sn, Cd, Ge, and/or an oxide of a combination thereof.

A gate insulating layer 104 is formed above the active layer 103. Thegate insulating layer 104 may include a single or multi-layer structureincluding an inorganic material, such as silicon oxide, silicon nitride,and/or the like. The gate insulating layer 104 insulates the activelayer 103 from the gate electrode 105.

The gate electrode 105 is formed above the gate insulating layer 104.The gate electrode 105 may be connected to a gate line applying anon/off signal to the TFT 110 a. The gate electrode 105 may include a lowresistance metallic material. The gate electrode 105 may include asingle or multi-layer structure including Al, Pt, Pd, Ag, Mg, Au, Ni,Nd, Ir, Cr, Li, Ca, Mo, Ti, W, and Cu, and/or the like.

An interlayer insulating layer 106 is formed above the gate electrode105. The interlayer insulating layer 106 insulates the source electrode107 and the drain electrode 108 from the gate electrode 105. Theinterlayer insulating layer 106 may include a single or multi-layerstructure including an inorganic material. For example, the inorganicmaterial may include metallic oxide or metallic nitride. For example,the inorganic material may include SiO₂, SiNx, SiON, Al₂O₃, TiO₂, Ta₂O₅,HfO₂, ZrO₂, and/or the like.

The source electrode 107 and the drain electrode 108 are formed abovethe interlayer insulating layer 106. The source electrode 107 and thedrain electrode 108 may each include a single or multi-layer structureincluding Al, Pt, Pd, Ag, Mg, Au, Ni,

Nd, Ir, Cr, Li, Ca, Mo, Ti, W, Cu, and/or the like. The source electrode107 and the drain electrode 108 contact regions of the active layer 103.

A passivation layer 109 may cover the TFT 110 a. The passivation layer109 resolves a step difference originated from the TFT 110 a, planarizesthe upper surface thereof, and thus prevents or substantially prevents adefect from occurring to the display element 110 b due to lowerirregularities.

The passivation layer 109 may include a single or multi-layer structureincluding an organic material. The organic material may include ageneral purpose polymer such as polymethylmethacrylate (PMMA) orpolystylene (PS), polymer derivatives having a phenol-based group, anacryl-based polymer, an imide-based polymer, an aryl ether-basedpolymer, an amide-based polymer, a fluorine-based polymer, ap-xylene-based polymer, a vinyl alcohol-based polymer, and/or a blendthereof. Also, the passivation layer 109 may include a composite stackedlayer of an inorganic insulating layer and an organic insulating layer.

The display element 110 b is formed above the passivation layer 109. Thedisplay element 110 b includes a first electrode 111, a second electrode113 facing the first electrode 111, and an intermediate layer 112between the first electrode 111 and the second electrode 113.

The first electrode 111 may be electrically connected to the drainelectrode 108. The first electrode 111 may have various suitable shapesand, for example, may be patterned in an island shape.

The first electrode 111 may be formed above the passivation layer 109and electrically connected to the TFT 110 a via a contact hole formed inthe passivation layer 109. The first electrode 111 may be, for example,a reflective electrode. For example, the first electrode 111 may includea reflective layer including Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr,and/or a compound thereof, and a transparent electrode layer formedabove the reflective layer. The transparent electrode layer may includeindium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), In₂O₃(indium oxide), indium gallium oxide (IGO), aluminum zinc oxide (AZO) ,and/or the like.

The second electrode 113 facing the first electrode 111 may be atransparent electrode and may include a metallic thin film having asmall work function and including Li, Ca, LiF/Ca, LiF/AI, Al, Ag, Mg,and/or the like, and a compound thereof. Also, an auxiliary electrodelayer or a bus electrode may be further formed by using ITO, IZO, ZnO,or, In₂O₃, and/or the like above the metallic thin film. Therefore, thesecond electrode 113 may transmit light emitted from the organicemission layer included in the intermediate layer 112. That is, lightemitted from the organic emission layer may be directly emitted towardthe second electrode 113 or reflected by the first electrode 111including the reflective electrode and emitted toward the secondelectrode 113.

However, the display portion 110 according to an embodiment is notlimited to a top-emission type display portion, and may be abottom-emission type display portion that emits light emitted from anorganic emission layer toward the base substrate 101. In this case, thefirst electrode 111 may include a transparent electrode, and the secondelectrode 113 may include a reflective electrode. Also, the displayportion 110 according to an embodiment may be a dual-emission typedisplay portion that emits light in a dual direction including the topdirection and the bottom direction.

A pixel-defining layer 119 including an insulating material is formedabove the first electrode 111. The pixel-defining layer 119 may includeat least one of an organic insulating material including polyimide,polyamide, an acryl resin, benzocyclobutene (BCB), and/or the like, anda phenol resin, and may be formed by using a method such as spincoating. The pixel-defining layer 119 exposes a set or predeterminedregion of the first electrode 111, and the intermediate layer 112including the organic emission layer is located in the exposed region.That is, the pixel-defining layer 119 defines a pixel region of anorganic light-emitting device. The pixel-defining layer 119 may be thestep portion S (see, e.g., FIG. 2) illustrated in, and described inreference to, FIGS. 1 to 6, and the buffer layer 210 may reduce a stepdifference by the pixel-defining layer 119.

The organic emission layer included in the intermediate layer 112 mayinclude a low molecular organic material or a polymer organic materialand selectively further include a functional layer, such as a holetransport layer (HTL), a hole injection layer (HIL), an electrontransport layer (ETL), and an electron injection layer (EIL), inaddition to the organic emission layer.

FIG. 8 is a cross-sectional view illustrating another example of theportion of the display device 10 taken along the line I-I′ of FIG. 1.

Referring to FIG. 8, the display device 10 may include the displaysubstrate 100, and the thin film encapsulation layer 200 above thedisplay substrate 100.

The display substrate 100 may include a base substrate 101 and thedisplay portion 110 above the base substrate 101. The display portion110 may include the TFT 110 a and the display element 110 b. Also, thethin film encapsulation layer 200 prevents or substantially preventsexternal oxygen, moisture, and/or the like from penetrating into thedisplay portion 110 by sealing the display portion 110 and may includethe buffer layer 210 and the barrier layer 220.

Because the thin film encapsulation layer 200 of the display portion 110is the same or substantially the same as that illustrated in anddescribed with reference to FIGS. 1 to 7, description thereof may not berepeated.

Referring to FIG. 8, the display device 10 may further include aprotective layer 300 above the display portion 110. The displaysubstrate 100 may further include a capping layer 120 between theprotective layer 300 and the second electrode 113 of the display element110 b.

The protective layer 300 may include the same or substantially the samematerial as that of the buffer layer 210. That is, the protective layer300 may include silicon oxide including carbon and hydrogen. Forexample, the plurality of sub-layers 222 may include a material having acomposition formula of SiOxCyHz. However, the protective layer 300 mayhave properties closer to an inorganic layer compared to the bufferlayer 210. For example, the protective layer 300 may include content ofoxygen greater than that of the buffer layer 210 and include content ofcarbon less than that of the buffer layer 210, and further include asilicon carbide to which hydrogen is coupled.

When the protective layer 300 has the properties of the inorganic layeras described above, an outgassing phenomenon reduces during a process offorming the protective layer 300, and thus the display element may beprevented or substantially prevented from being damaged by the emittedgas.

The protective layer 300 may be formed by using the same method as themethod used for forming the buffer layer 210. That is, before the thinfilm encapsulation layer 200 is formed, a raw gas and a reaction gas areinjected into the chamber in which the display substrate 100 is located,and the protective layer 300 may be formed by using the PECVD. In thiscase, to allow the protective layer 300 to have properties close to aninorganic layer, flux of oxygen, which is a reaction gas introduced intothe chamber when forming the protective layer 300, may be greater thanflux of oxygen introduced into the chamber when forming the buffer layer210. Therefore, both the protective layer 300 and the thin filmencapsulation layer 200 may be formed in one chamber by using the samemethod.

The capping layer 120 is formed above the second electrode 113 andprotects the display element 110 b, and assists light generated from thedisplay element 110 b so that the light may be efficiently emitted. Forexample, the capping layer 120 may include an organic material such asa-NPD, NPB, TPD, m-MTDATA, Alq₃, and/or CuPc. In this case, the cappinglayer 120 may have a refractive index ranging from about 1.6 to about3.0. However, embodiments of the present invention are not limitedthereto, and the capping layer 120 may include a material that may blockmoisture and/or oxygen.

The protective layer 300 including the same or substantially the samematerial as that of the buffer layer 210 may have a refractive indexless than that of the capping layer 120. For example, the protectivelayer 300 may have a refractive index ranging from about 1.38 to about1.5. When fluorine (F) is further added to the protective layer 300, theprotective layer 300 may have a lower refractive index. When theprotective layer 300 has a small refractive index as described above,extinction of light generated from the display element 110 b during aprocess of being emitted to outside may be suppressed and thuslight-extraction efficiency of the display device 10 may improve (e.g.,increase).

FIG. 9 is a cross-sectional view illustrating another example of theportion of the display device 10 taken along the line I-I′ of FIG. 1;and FIG. 10 is a cross-sectional view illustrating an example of aportion of the display device 10 taken along the line II-II′ of FIG. 1.

Referring to FIGS. 9 and 10, the display device 10 may include thedisplay substrate 100 and the thin film encapsulation layer 200 abovethe display substrate 100.

The display substrate 100 may include the base substrate 101 and thedisplay portion 110 above the base substrate 101. The display portion110 may include the TFT 110 a and the display element 110 b. Because thedisplay portion 110 is the same or substantially the same as thatdescribed with reference to FIG. 7, description thereof may not berepeated.

The thin film encapsulation layer 200 seals the display portion 110, andmay include a first barrier layer 230, the buffer layer 210, and asecond barrier layer 220 that are sequentially stacked.

The buffer layer 210 may include about 20 to about 50 atomic % ofsilicon, about 10 to about 40 atomic % of oxygen, and about 30 to about60 atomic % of carbon based on a total number of atoms of silicon,oxygen, and carbon. Also, in an embodiment, the buffer layer 210 mayinclude about 30 to about 40 atomic % of silicon, about 18 to about 28atomic % of oxygen, and about 40 to about 50 atomic % of carbon. In anembodiment, the buffer layer 210 may include about 33 to about 36 atomic% of silicon, about 20 to about 23 atomic % of oxygen, and about 42 toabout 45 atomic % of carbon. Therefore, the buffer layer 210 may reducea step difference (e.g., a step height) formed by the pixel-defininglayer 119 and prevent or substantially prevent an air gap from beingformed between the step difference and the thin film encapsulation layer200.

The second barrier layer 220 may include silicon nitride, aluminumnitride, zirconium nitride, titanium nitride, hafnium nitride, tantalumnitride, silicon oxide, aluminum oxide, titanium oxide, tin oxide,cesium oxide, silicon oxynitride (SiON), and/or the like.

For example, the first barrier layer 230 may include the same orsubstantially the same material as that of the second barrier layer 220.

In another embodiment, the first barrier layer 230 may include the sameor substantially the same material as that of the buffer layer 210. Inthe case where the first barrier layer 230 includes the same orsubstantially the same material as that of the buffer layer 210, thefirst barrier layer 230 may include the greater amount of an inorganicmaterial than that of the buffer layer 210. The first barrier layer 230and the buffer layer 210 may be successively formed inside the samechamber by using the same deposition method. However, when depositingthe first barrier layer 230, the hardness of the first barrier layer 230may improve (e.g., increase) by increasing the flux of oxygen (which isa reaction gas), as compared to the deposition of the buffer layer 210.

As illustrated in FIG. 10, the first barrier layer 230 and the secondbarrier layer 220 may extend further than the buffer layer 210 and maycontact each other at the outer portion of the buffer layer 210. Also,at least one of the first barrier layer 230 and the second barrier layer220 may contact the gate insulating layer 104 and the interlayerinsulating layer 106 at the outer portion of the buffer layer 210.Therefore, transmission of external moisture via the lateral side may beprevented or substantially prevented, and adhesive force of the thinfilm encapsulation layer 200 may improve (e.g., increase).

Also, the display substrate 100 may further include a dam D at the edgeof the base substrate 101. The dam D may be formed in a non-displayarea, which is outside of the display area in which the display element110 b is disposed. A voltage line P may be disposed in the non-displayarea and connected to the second electrode 113 via a wiring 116.However, embodiments of the present invention are not limited thereto,and the voltage line P may directly contact the second electrode 113.

The dam D may include the same or substantially the same material asthat of at least one of layers including the gate insulating layer 104to the pixel-defining layer 119. The dam D may overlap and contact atleast the outer edge of the voltage line P including a metallicmaterial. Therefore, the dam D that includes an organic material havingexcellent adhesive force with respect to metal compared to an inorganicmaterial may be stably formed with excellent adhesive force.

The dam D may include a single layer or a plurality of layers. Forexample, the dam D may include a first layer including the same orsubstantially the same material as that of the passivation layer 109 anda second layer including the same or substantially the same material asthat of the pixel-defining layer 119 above the first layer. Also, thedam D may be provided in the plural. In the case where the dam D isprovided in the plural, the height of the dam D may increase toward theouter portion of the base substrate 101.

The dam D may prevent or substantially prevent the buffer layer 210 frombeing formed up to the edge of the base substrate 101. Because theprecursor layer for forming the buffer layer 210 may have liquidity tosome degree, the dam D may prevent or substantially prevent the edgetail of the buffer layer 210 from being formed by blocking the precursorlayer flowing toward the edge of the base substrate 101.

Therefore, the buffer layer 210 may face or contact the inner surface ofthe dam D. For another example, the buffer layer 210 may overlap aportion of the dam D but does not extend outside the dam D.

However, the first barrier layer 230 and the second barrier layer 220may cover the dam D. When the second barrier layer 220 includes the sameor substantially the same material as that of the buffer layer 210, thesecond barrier layer 220 includes many characteristics of an inorganiclayer compared to the buffer layer 210 and thus is formed conformally.Therefore, the liquidity of a precursor layer for forming the secondbarrier layer 220 is not problematic.

The first barrier layer 230 and the second barrier layer 220 may contacteach other at the outer portion of the dam D. Also, at least one of thefirst barrier layer 230 and the second barrier layer 220 may contact thegate insulating layer 104 or the interlayer insulating layer 106 at theouter portion of the dam D. Therefore, transmission of external moisturevia the lateral side may be prevented or substantially prevented andadhesive force of the thin film encapsulation layer 200 may improve(e.g., increase).

The display device 10 illustrated in FIGS. 9 and 10 may further includethe protective layer 300 (see, e.g., FIG. 8) and the capping layer 120(see, e.g., FIG. 8) illustrated in and described in reference to FIG. 8.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondiscussed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of theinventive concept.

Spatially relative terms, such as “below”, “lower”, “under”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or in operation, in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “under” otherelements or features would then be oriented “above” the other elementsor features. Thus, the example terms “below” and “under” can encompassboth an orientation of above and below. The device may be otherwiseoriented (e.g., rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein should be interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the inventive concept.As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include,”“including,” “comprises,” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list. Further, the use of“may” when describing embodiments of the inventive concept refers to“one or more embodiments of the inventive concept.”

Also, the term “exemplary” is intended to refer to an example orillustration.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent” another elementor layer, it can be directly on, connected to, coupled to, or adjacentthe other element or layer, or one or more intervening elements orlayers may be present. When an element or layer is referred to as being“directly on,” “directly connected to”, “directly coupled to”, or“immediately adjacent” another element or layer, there are nointervening elements or layers present.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent variations in measured orcalculated values that would be recognized by those of ordinary skill inthe art.

As used herein, the terms “use,” “using,” and “used” may be consideredsynonymous with the terms “utilize,” “utilizing,” and “utilized,”respectively.

Also, any numerical range recited herein is intended to include allsub-ranges of the same numerical precision subsumed within the recitedrange. For example, a range of “1.0 to 10.0” is intended to include allsubranges between (and including) the recited minimum value of 1.0 andthe recited maximum value of 10.0, that is, having a minimum value equalto or greater than 1.0 and a maximum value equal to or less than 10.0,such as, for example, 2.4 to 7.6. Any maximum numerical limitationrecited herein is intended to include all lower numerical limitationssubsumed therein and any minimum numerical limitation recited in thisspecification is intended to include all higher numerical limitationssubsumed therein. Accordingly, Applicant reserves the right to amendthis specification, including the claims, to expressly recite anysub-range subsumed within the ranges expressly recited herein. All suchranges are intended to be inherently described in this specification.

Though the inventive concept has been described with reference to theembodiments illustrated in the drawings, this is merely exemplary, andit will be understood by those of ordinary skill in the art that varioussuitable changes in form and details and equivalents thereof may be madetherein without departing from the spirit and scope of the inventiveconcept as defined by the following claims, and equivalents thereof.

What is claimed is:
 1. A display device comprising: a display substrate comprising at least one step portion; and a thin film encapsulation layer above the display substrate, the thin film encapsulation layer comprising a buffer layer, and the buffer layer comprising a plurality of sub-layers and interfaces between the plurality of sub-layers, each one of the sub-layers comprising a first portion and a second portion between the first portion and the display substrate, a carbon content of each one of the sub-layers gradually increasing from the first portion toward the second portion, wherein each of the plurality of sub-layers comprises about 20 to about 50 atomic % of silicon, about 10 to about 40 atomic % of oxygen, and about 30 to about 60 atomic % of carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.
 2. The display device of claim 1, wherein each of the plurality of sub-layers has a thickness from about 300 Å to about 10000 Å.
 3. The display device of claim 1, wherein an interval between two adjacent interfaces of the interfaces reduces toward a portion overlapping the step portion from the outer portion of the step portion.
 4. The display device of claim 1, wherein the buffer layer has a first thickness at a location spaced from the step portion and has a second thickness at a location overlapping the step portion, and wherein the second thickness is less than the first thickness and greater than or equal to 0.5 times the first thickness.
 5. The display device of claim 1, wherein an upper surface of the first portion forms an interface of the interfaces, and wherein the first portion has a silicon content ratio greater than that of the second portion, and the first portion has a carbon content ratio less than that of the second portion.
 6. The display device of claim 5, wherein each of the plurality of sub-layers comprises about 30 to about 40 atomic % of the silicon, about 18 to about 28 atomic % of the oxygen, and about 40 to about 50 atomic % of the carbon based on the total number of atoms of the silicon, the oxygen, and the carbon.
 7. The display device of claim 5, wherein each of the plurality of sub-layers comprises about 33 to about 36 atomic % of the silicon, about 20 to about 23 atomic % of the oxygen, and about 42 to about 45 atomic % of the carbon based on the total number of atoms of the silicon, the oxygen, and the carbon.
 8. The display device of claim 1, wherein the display substrate comprises a base substrate and a display portion above the base substrate, wherein the display portion comprises a plurality of display elements and a pixel-defining layer defining a light-emitting region of the plurality of display elements, and wherein the at least one step portion comprises the pixel-defining layer.
 9. The display device of claim 8, further comprising a protective layer above the display portion, the protective layer comprising a same material as that of the buffer layer.
 10. The display device of claim 9, wherein each of the plurality of display elements comprises a first electrode, a second electrode, and an intermediate layer between the first and second electrodes, the intermediate layer comprising an organic emission layer, and wherein the display substrate further comprises a capping layer between the first electrode and the protective layer, the capping layer having a refractive index greater than that of the protective layer.
 11. The display device of claim 10, wherein the protective layer has a refractive index from about 1.38 to about 1.5.
 12. The display device of claim 9, wherein the protective layer further comprises silicon carbide to which hydrogen is coupled.
 13. The display device of claim 8, wherein the thin film encapsulation layer further comprises a barrier layer above the buffer layer.
 14. The display device of claim 13, wherein the thin film encapsulation layer is configured to seal the display portion, wherein the barrier layer comprises a first barrier layer and a second barrier layer overlapping each other with the buffer layer therebetween, and wherein the first and second barrier layers comprise an inorganic layer.
 15. The display device of claim 14, wherein the first and second barrier layers contact each other at an outer portion of the buffer layer.
 16. A method of manufacturing a display device, the method comprising: forming a display portion above a base substrate; and forming a thin film encapsulation layer sealing the display portion, the forming of the thin film encapsulation layer comprising: injecting a raw gas and a reaction gas inside a chamber in which the base substrate is located, depositing a precursor layer above the base substrate by utilizing plasma-enhanced chemical vapor deposition, and forming a sub-layer by curing the precursor layer utilizing plasma; forming a plurality of sub-layers and forming a buffer layer in which the plurality of sub-layers are stacked; and forming a barrier layer above the buffer layer inside the chamber, wherein the plurality of sub-layers comprise a silicon oxide comprising carbon and hydrogen, and wherein each of the plurality of sub-layers comprise about 20 to about 50 atomic % of silicon, about 10 to about 40 atomic % of oxygen, and about 30 to about 60 atomic % of carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.
 17. The method of claim 16, wherein the raw gas comprises hexamethyldisiloxane, and the reaction gas comprises oxygen, nitrous oxide, and/or hydrogen.
 18. The method of claim 16, wherein the buffer layer comprises interfaces between the plurality of sub-layers, wherein each of the plurality of sub-layers comprises a first region and a second region above the first region, an upper surface of the second region forming an interface of the interfaces, wherein the second region has a silicon content ratio greater than that of the first region, and the second region has a carbon content ratio less than that of the first region.
 19. The method of claim 18, wherein each of the plurality of sub-layers comprises about 30 to about 40 atomic % of the silicon, about 18 to about 28 atomic % of the oxygen, and about 40 to about 50 atomic % of the carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.
 20. The method of claim 18, wherein each of the plurality of sub-layers comprises about 33 to about 36 atomic % of the silicon, about 20 to about 23 atomic % of the oxygen, and about 42 to about 45 atomic % of the carbon based on a total number of atoms of the silicon, the oxygen, and the carbon.
 21. The method of claim 18, wherein the display portion comprises at least one step portion above a surface thereof, and wherein the buffer layer has a first thickness at a location spaced from the step portion and a second thickness at a location overlapping the step portion, the second thickness being about 0.5 times or more than and less than about one times the first thickness.
 22. The method of claim 21, wherein the interfaces are formed in a curved surface changing from a concave shape to a convex shape toward a portion overlapping the step portion from an outer portion of the step portion.
 23. The method of claim 21, wherein an interval between two adjacent interfaces of the interfaces increases toward the display portion in an outer portion of the step portion.
 24. The method of claim 21, wherein an interval between two adjacent interfaces of the interfaces reduces toward a portion overlapping the step portion from an outer portion of the step portion.
 25. The method of claim 16, wherein each of the plurality of sub-layers has a thickness from about 300 Å to about 10000 Å.
 26. The method of claim 16, further comprising: before the forming of the thin film encapsulation layer, forming a protective layer above the display portion, wherein the protective layer comprises a same material as that of the sub-layer and being formed by utilizing a same method as the sub-layer, and wherein flux of oxygen introduced into the chamber while the protective layer is formed is greater than that of oxygen introduced into the chamber while the sub-layer is formed.
 27. The method of claim 26, wherein the protective layer further comprises silicon carbide to which hydrogen is coupled.
 28. The method of claim 26, wherein the protective layer has a refractive index from about 1.38 to about 1.5.
 29. The method of claim 28, wherein the display portion comprises a plurality of display elements, each comprising a first electrode, a second electrode, and an intermediate layer between the first and second electrodes, the intermediate layer comprising an organic emission layer, and wherein the display device comprises a capping layer between the second electrode and the protective layer, the capping layer having a refractive index greater than that of the protective layer. 